The plants to which the present invention relates comprise a closed circuit in which a refrigerant circulates, the latter being driven by means of a compressor of the lubricated type. Because of the lubrication requirements of the compressor, it is known to introduce a lubricating oil into it.
Correct operation of the plant is determined by a clean state of the internal surfaces of the circuit. It is up to its operator to eliminate any impurities liable to be entrained by the refrigerant. The origin of the formation of these impurities lies in incidents in the operation of the motor in sealed units or accessible sealed units and the formation of scale as a result of these, the presence of water in the circuit, the formation of acid, the degradation of the lubricating oil or else the formation of oxides at welded or brazed joints when they were produced without having removed beforehand any oxygen trapped in the pipes.
A cleaning operation is therefore already necessary upon commissioning a new plant, or subsequently after a fault that has contaminated the circuit has been repaired.
Hitherto, the Applicant has used for these cleaning operations a product of the R141b type, that is to say a 1,1-dichloro-1-fluoroethane, having a high solvent power (KB=51) and a low surface tension (18.4 mN/m), this product being suitable for cleaning the surfaces of metals, plastics and composites. In the liquid state, it is not inflammable and it is packaged in 28 kg bottles pressurized under dry nitrogen (7 bar). To carry out cleaning, the liquid outlet of the bottle is connected to the component of the plant to be cleaned, for example a tube exchanger. The outlet of the component is connected to a recovery drum via a hose. This drum is itself maintained at atmospheric pressure, being connected to the open air via a nozzle that allows the nitrogen and any vapours of the product to be discharged. Venting is sufficient since the product has, under the operating conditions, a low vapour pressure, its boiling point being above 30° C.
The cleaning operation consists in circulating the fluid by opening the tap on the bottle. The fluid is then propelled by the pressurized gas. Optionally, the circulation is activated with the creation of pressure surges in the fluid, by rapidly and repeatedly opening and closing the valve. The supply of fluid is stopped when the liquid recovered in the drum runs clear. The plant is then clean.
Because of the regulations now in force limiting the use of HCFC fluids, it has become necessary to use a replacement product.
The replacement product must have the same properties as the previous one. It must be a solvent for the products involved in the plants, must not be inflammable under the operating conditions, must be extractable, must have a low viscosity and not leave residual traces or at least traces compatible with the refrigerants and lubricating oils used in the refrigeration circuit. It must also be inexpensive.
Cleaning oils based on a polyol-ester (POE) or especially a polyalkylene glycol (PAG), that have the stripping properties and the low viscosity that are required for this application, are known. They are also compatible with the refrigerant used in the circuit. In particular, they are used for the conversion of plants to take the new statutory refrigerants. In circulation in a closed circuit, the amount is around 1%, at most 3%. However, their use in cleaning operations, where they are used in more substantial proportions, is unsatisfactory as they are very difficult to extract from the circuit. Furthermore, a non-extractable oil residue remains, which may impair proper operation or even cause machine breakage.
The subject of the invention is therefore a cleaning fluid for refrigeration plants that does not have this drawback.